"She's toned up and lost a few pounds over the last two years," he says.

The exercise classes at the club are designed to give both dogs and their owners a cardio workout and strength training.

"You have to do it together, so you strengthen the human-animal bond," says Tricia Montgomery, K9 Fit Club's founder and president. "We as the pet owner must be the one to get our dogs motivated and moving by working out with them."

K9 Fit has eight gyms across the country. It recently started an online certification program for people who want to become human-canine fitness trainers. About 200 have passed the course so far.

Know your options

Dog gyms range from small family-owned businesses to franchise operations with all the latest equipment and places to groom your dog. The quality of the staff and the courses offered vary greatly from place to place. There may be a monthly membership fee. Expect to pay $100 or more for specific classes.

Some of the new canine sports gyms are mighty impressive. Frolick Dogs, a new 5,000 square foot facility in Alexandria, Va., has doggie treadmills, balance platforms and lots of colorful rubber peanuts—stability balls designed for dogs—that help build their core and leg muscles.

There's also a large space for agility training. All the obstacles—the jumps, hoops, tunnels, teeter totter, balance beam and weave posts—are regulation-size for those who plan to enter their dogs in competition.

At K9 Fit Club people and pets work out together. Exercise classes are designed to give both dogs and their owners a cardio workout and strength training.

Co-owner and professional dog trainer Kevin Gilliam is there to explain how to use the equipment and coach owners on ways to encourage their dogs to try new things.

"People come in the first time and they don't know what to do or the dog is a little bit shy. And the next time they come back the dog is pulling them in here. That's fun to see," Gilliam says.

Kathy McAfee and her three-year-old Portuguese Water Dog Lilly recently joined Frolick Dogs after McAfee broke her ankle, derailing their regular long walks together.

"She's a show dog and she needs to get back in shape and this place will let me do that," McAfee says. "It took a little coaxing at first to get her to stay on the treadmill, but now she loves it."

The All Dogs Gym & Inn in Manchester, N.H. offers people-pet exercise classes as well as doggie day care exercise programs. Owner Gail Fisher is a certified dog behavior consultant and author of the book The Thinking Dog. She believes the interaction between owner and pet at the gym helps build a strong relationship.

"It's a very good outlet for their energy—and it's also fun for the people," Fisher says. "You're training the dog in a way that exercises the dog physically and mentally, and it gets you up and moving as well."

"We're feeding them too many calories each day and they're not getting enough physical exercise," says veterinarian Dr. Ernie Ward, who founded the association. "This is the number one health threat our pets face today and it's completely preventable."

Dr. Marty Becker of Vetsreet.com and author of the book Fitness Unleashed!, warns that obesity can lead to serious health problems for pets, including diabetes, joint problems and heart disease—even an increased risk of cancer.